An operation mode selection unit selects an operation mode of a power converter and generates a mode selection signal indicating the result of selection, in accordance with a load condition and a power supply condition. An operation mode switching control unit generates a mode control signal designating an operation mode of the power converter. When the operation mode currently selected by the mode control signal is different from an operation mode indicated by the mode selection signal, the operation mode switching control unit adjusts a power distribution ratio between a plurality of DC power supplies or an output voltage on an electric power line so as not to change abruptly, and then permits a transition of operation mode.